无变压器MMC交流故障穿越策略

AC fault ride-through strategy for transformer-less MMC

基于模块化多电平换流器(Modular Multilevel Converter,MMC)的柔性技术是实现城市分区电网互联的新技术,针对目前双联接变压器半桥子模块MMC和单联接变压器混合子模块MMC的柔性互联装置造价高和占地面积大的缺点,提出了一种基于无变压器混合子模块MMC的供电分区柔性互联装置.分析了装置连接的分区电网间零序电流特性,设计了一种基于比例谐振控制器的零序电流抑制策略.针对电网故障时,非故障相电压抬升对装置运行特性的影响,指出了一种降低直流电压的控制方法,并给出了电网故障时直流电压参考值和装置MMC桥臂全桥子模块占比的设计方案.在基于RT-LAB的半实物实验平台上进行了实验,实验结果表明电网单相对地故障时分区电网间的零序电流为零,装置仍然可以实现75%额定功率的传送,验证了本文直流电压参考值和全桥子模块占比设计的正确性以及交流故障穿越策略的有效性.

The flexible technology based on Modular Multilevel Converter(MMC)is a new technology to realize the interconnection of urban partitioned grid.To address the disadvantages of high cost and large volume of the partition flexible interconnection devices on double-transformers half-bridge power modules(PMs)MMC and single-transformer hybrid PMs MMC,a partition flexible interconnection device in power grid based on transformer-less hybrid PMs MMC is proposed in this paper.The characteristics of the zero sequence current between two partition grids connected by the device are analyzed.And a zero-sequence current suppression strategy based on proportional resonant is designed.In view of the impact of the non-fault phase voltage rise at AC fault situation on the operating characteristics of the device,a control strategy to reduce the DC voltage is proposed,and the reference value of DC voltage during AC fault period and the design method of full-bridge PMs MMC ratio are also presented.The experiments are conducted on the semi-physical experiment platform based on RT-LAB.The experimental results show that during a single-phase AC ground fault,the zero-sequence current between the grid partitions is zero,and the device can still transfer 75%of the rated power,which verifies the correctness of the design of the DC voltage reference value and the ratio of full-bridge PMs as well as the effectiveness of the AC fault ride-through strategy.